This intro change the background the Left 4 Dead 2, well you already know how install it, but if you don't know then here this.
How install the background to Left 4 Dead 2?
The first step that you have that make is extract the file .vpk after drag the file at your desktop or anywhere you want.
The second step is copy five times the file .bik but with different name.
Examples
l4d2_background01
l4d2_background02
l4d2_background03
l4d2_background04
l4d2_background05
That is all.
The third step is copy the five files and paste them in the folder media of the game.
The fourth step: Enjoy it.